GeoServer is an open source software server written in Java that allows users to share and edit geospatial data. Designed for interoperability, it publishes data from any major spatial data source using open standards: WMS, WFS, WCS, WPS and REST

JasperReports Library, the world's most popular open source business intelligence and reporting engine and JasperReports Server, the most popular open source interactive report server built-on JasperReports Library

iText is a PDF library that allows you to CREATE, ADAPT, INSPECT and MAINTAIN documents in the Portable Document Format (PDF):
- Generate documents and reports based on data from an XML file or a database
- Create maps and books, exploiting numerous interactive features available in PDF
- Add bookmarks, page numbers, watermarks, and other features to existing PDF documents
- Split or concatenate pages from existing PDF files
- Fill out interactive forms
- Serve dynamically generated or manipulated PDF documents to a web browser
iText is used by Java, .NET, Android and GAE developers to enhance their applications with PDF functionality.
Several iText engineers are actively supporting the project on StackOverflow: http://stackoverflow.com/questions/tagged/itext

HSQLDB is a relational database engine written in Java, with a JDBC driver, conforming to ANSI SQL:2011. A small, fast, multithreaded engine and server with memory and disk tables, LOBs, transaction isolation, multiversion concurrency and ACID.

Ajax+Mobile Java Web framework. With 200+ Ajax components and event-driven, Ajax/RIA apps are as effortless and rich as desktop apps and HTML/XUL pages. Support JSP/JSF/JavaEE/Spring, Ajax Push and Client-fusion; also Java/Groovy/Python/JavaScript.

YTD2 is a free Java application for downloading youtube videos as flv/mp4 files. Should run on all platforms where Java is supported. GNU General Public License V3. Using hc.apache.org components. Based on the idea of "ytd" by rafalfr

A web based Geographic Metadata Catalog for data description and discovery. It implements international standards (e.g. ISO19115/19139, ISO19115-3, Z39.50, CSW 2.0, OGC). It originates from the United Nations and is used by many governments as geoportal software
Source code available on github https://github.com/geonetwork/